Structures such as dwellings and low rise buildings commonly do not have foundations which are in direct contact with stable load bearing underground strata, such as, for example, bedrock. Often, these structures have a footing which forms the basis upon which the foundation wall rests. The footing is usually wider than the foundation wall in order to distribute the structure's weight over a greater soil area. Alternately, a structure's foundation may consist of a floor slab. The structure 's position and stability thus depends on the stability of the underlying soil. In time, soil conditions may change, due to, for example, ground movement, ground water level changes or soil compaction. Changes in soil conditions or catastrophic events, such as, for example, earthquakes may result in highly undesirable settling of the structure, causing the structure to become uneven with the horizontal plane of the earth. Settling of the structure may result in structural damage, loss of real estate value and major inconvenience to the user of the structure.
Various devices and methods have been developed to raise and support a structure such as a building where settling of the foundation has occurred. Generally, these devices and methods employ foundation lifting, also known as jacking, equipment such as hydraulicly operated jacks in conjunction with piers, also known as piles or pilings. One or more piers are driven into the ground by means of one or more hydraulic jacks until the pier reaches bedrock or until the pier's frictional resistance equals the compression weight of the structure. Additional lift action then raises the foundation. When the desired foundation level is reached, the pier is permanently attached to the foundation and the hydraulic lift mechanism is removed. These methods typically require excavation of a hole adjacent to or underneath the foundation in order to position and operate the lifting equipment.
U.S. Pat. No. 5,269,630 (Bolin et al., 1993) discloses an apparatus for lifting and stabilizing a structural slab overlying the ground using hydraulic cylinders. A base is attached to the slab, hydraulic cylinders are supported from the base. Piston rods are connected to a head assembly containing a slip clamp which firmly grabs a pier segment. A retraction stroke of the hydraulic cylinders drives the pier into the ground through a hole in the slab. The pier is permanently attached to the base when the slab is lifted to the required level.
U.S. Pat. No. 5,246,311 (West et al., 1993) discloses a foundation repairing system including a pier driver, secondary lilting mechanisms, a pier head and pier sections. The pier head is bolted to the foundation. The pier driving means includes a hydraulic piston-and-cylinder arrangement which is rigidly connected to a pier driving bracket comprising an opposing pair of upright members and a foot member which is fitted underneath the pier head. The piston rod of the hydraulic jack is fitted with an adapter for mating with the distal end of a pier section. A pier section is guided through a sleeve attached to the pier head, fitted onto the adapter and forced downward by the hydraulic jack. Additional pier sections can be fitted end-to-end and driven down until the necessary resistance is encountered from the underlying ground which is sufficient to support the foundation. The pier driver is then removed and a secondary lifting mechanism is affixed to the pier guide to raise the foundation to the desired level. The pier is then permanently attached to the pier guide sleeve.
U.S. Pat. No. 5,234,287 (Rippe, Jr., 1993) discloses a foundation raising and securing apparatus and process wherein a jacking apparatus is coupled to a bracket which is attached to the foundation. The jacking apparatus comprises a hydraulic jack connected to tie-bars which are fastened to a cradle. The cradle is removably coupled to the bracket having a sleeve. The distal end of the ram is provided with a head for compressibly engaging a pier. Pier sections are placed in the jacking apparatus, guided through the sleeve and driven into the ground by hydraulic pressure. Pier sections can be connected end-to-end. Once the pier sections have reached the desired depth, the upper section is permanently attached to the sleeve.
U.S. Pat. No. 5,154,539 (McCown, Sr. et al., 1992) discloses a foundation shoring and stabilizing apparatus wherein pier sections are driven into the ground using a hydraulic jack. A support bracket including a guide member is attached to the foundation. A lifting cradle engages the support bracket. The support cradle is removably attached to the bottom ends of two upright members. A yoke assembly is removably attached to the upper portions of the upright members. A pier driving means, such as a hydraulic cylinder is rigidly attached to the yoke assembly. A piling adapter is mounted to the distal end of the piston rod. A pier section is placed into the guide member and positioned between the upright members wherein the top of the pier is in contact with the downward facing piling adapter of the hydraulic jack. Downward extension of the piston rod forces the pier into the ground and lifts the cradle once the pier sections have reached bedrock. The yoke assembly can be re-positioned at different heights on the upright members in order to move the hydraulic jack to different positions relative to the cradle. Pins are used to restrain the upright members from pivoting outward.
U.S. Pat. No. 4,925,345 (McCown, Jr. et al., 1990) discloses an apparatus for stabilizing and elevating the foundations of buildings using pier sections which are driven down by a pair of power cylinders such as hydraulic jacks. The hydraulic cylinders are attached to an upper head assembly by means of a pair of mounting plates extending laterally from a slip clamp, using clevis connectors and pins. Connecting rods are attached to the upper head assembly and a lower cross arm using clevis connectors. The lower cross arm is mounted to a foundation bracket and a tubular guide sleeve. A pier is fitted through a guide sleeve of the upper head assembly, the slip clamp and the tubular guide sleeve. Upon extending the power cylinders, the slip bowl grips the pier and forces it into a ground.
U.S. Pat. No. 4.911,580 (Gregory et al., 1990) discloses an apparatus and method for raising and supporting a foundation utilizing a pair of hydraulic ram units. Hydraulic cylinders are connected by means of clevis connectors to a pair of mounting plates extending from a lifting arm which is abutted underneath the foundation. The hydraulic rods are connected by means of clevis connectors to horizontal plates of a driving assembly which includes a slip bowl for clamping the pipe when the hydraulic rods are driven in a downward direction. A pair of threaded rods is welded to the lifting arm mounting plates. A pier section support sleeve is connected to a foundation lifting arm. Pier sections are driven into the ground by means of the hydraulic ram units. When the desired foundation level is obtained, the top of the upper pier section is secured to the lifting arms by means of the threaded rods.
It is well known to those skilled in the art that serious difficulties are experienced in practicing the art exemplified in the above referenced patents. Some of these difficulties result from the fact that the foundation lifting and securing process is usually carried out in the confinement of a relatively small excavation. The very limited working space makes it difficult to assemble the equipment, lift and secure the foundation and finally disassemble the equipment. Typically, it is desirable to use equipment which requires the lowest possible vertical clearance. For example, the hydraulic jacks used in pairs in patents '345 and '580 require less vertical clearance than the devices used in patents '287, '311 and '539, because the '345 and '580 hydraulic jacks are positioned parallel to the pier sections while the '287, '311, '539 single hydraulic jacks are supported above and directly in line with pier sections to be driven into the ground.
One particularly troublesome and costly problem involves binding or jamming of pier sections or lift equipment during the lifting or securing. This occurs where the longitudinal axis of a pier section is not in close alignment with the direction in which force is applied to the pier. The mis-alignment manifests itself in binding or jamming of a pier section with such equipment members as guide sleeves and slip bowls. When this occurs it may be necessary to cut the pier or the lift equipment components, resulting in costly delays or the replacement of lift equipment components. Lifting devices employing two parallel hydraulic jacks are particularly prone to mis-alignment because the two jacks may have slightly different performance characteristics, particularly after extensive use of the jacks. These performance differences can result in a difference in ram extension between the two jacks, thereby forcing the pier slip coupling or the pier compression coupling out of alignment with the pier. Single hydraulic jack lifting devices are known to jam against the building structure because of mis-alignment between the pier and the hydraulic jack. For example, U.S. Pat. No. 4,708,528 (Rippe, 1987) teaches that misalignment between the pier and the jacking cylinder causes excessive bending stresses, tilting the jacking equipment against the foundation wall. Known lifting devices and methods have not provided a fully effective solution to the recurring problem of jamming of pier sections or equipment components.
Accordingly, the need exists for devices and methods for lifting and securing structures, such as foundations and slabs, having improved alignment between the pier and the direction in which force is applied to the pier.